Various devices have been invented for the purpose of generating steam directly, by injecting water into a plenum which forms the combustion chamber for an air and fuel mixture. These devices have been designed to produce steam without heating a containing device filled with water, and thereby obviate the problem of heat energy loss from unintended transfer to the containing device, and thence to the surroundings.
In general, these devices all operate by first providing a combustion chamber into which hydrocarbon fuel and air are mixed, thence igniting the fuel and air mixture with a sparking mechanism. Simultaneously, a stream of water is directed into the chamber and into the flame. Energy from the flame is transferred to the water, producing steam. Steam is transferred, along with the products of combustion, out of the chamber and into a pipe or some other conveyance means to a place or to a device which uses the steam.
These devices are arranged so that the water is introduced onto the periphery of the incandescent envelope formed by fuel- air combustion. By doing so heat energy is transferred to the water and is quickly removed from the chamber with combustion effluents, and, in the process, combustion chamber walls are kept relatively cool.
It will be appreciated that one of the problems with such an arrangement is that without precise control of water flow, the injected water can easily collapse the incandescent envelope and extinguish the flame. Therefore, in addition to maintaining control over the stochiometric requirements for efficient combustion, operation of the device requires dynamically maintaining a fine balance between the pressure of the incandescent envelope and the pressure of injected water as the flow rate and volume of injectants change. Furthermore when these devices must operate over a wide range of requirements and must respond quickly to changing demand for steam volumes and temperatures, maintaining this balance becomes even more critical.